1. Field of the Invention
THIS INVENTION relates to hydraulic tensioning jacks to tension fasteners; tensioning systems for the fasteners; and structures and accessories for use therewith.
2. Prior Art
The principles of applying bolt tensile loadings using hydraulic means to generate precise amounts of force are well known and established. In general, use of such equipment requires that bolts be extended above the nut to allow the tensioner's puller to attach. In many instances, this may not be possible or desirable. For example, the bolts securing turbines and other steam generating equipment are expensive to replace, and longer bolts would require extensive modification of heat shielding and ancillary equipment. I have previously proposed a method of providing a coupling to the bolts, which would permit the use of hydraulic tensioning apparatus with such equipment, in International Publication WO 00/51791 (=PCT/AU00/00138).
Clearly, such a coupling must be capable of transmitting the extremely high force necessary to elongate the bolt shank.
Tapered threaded couplings are known, and are commonly used in applications such as coupling “pin & box” ends for drill rods. However, the restricted available dimensions and extreme load requirements of high strength bolted joints mean that a coupling made to these designs would be incapable of carrying such forces, were they manufactured to fit into such limited spaces.
Normal tapered thread constructions have limitations:—
the load carrying capacity for nominal sectional area is too low; and
the included flank angles of threads deflect forces radially outwards.
When used in a standard format by other manufacturers for bolt tensioning on steam turbines, these thread forms proved ineffective and dangerous, with many breaking and “launching” the tensioner assembly skywards.